Such a hair treatment device is known from EP-Bl 0052 325. The winding mandrel has a smooth surface. Hair is wound up on it. At the same time it can be subjected tangentially to the flow of heated air coming from the outflow nozzle of a hair dryer. The winding mandrel is equipped with openings which are connected to a negative pressure source, so that the hot air flowing from the hair dryer can be sucked away through the hair via a suction air channel and a suction circuit. In this manner the hair wound on the winding mandrel is dehumidified, dried and shaped rapidly.
The hair is received by the rotating winding mandrel due to the negative pressure taking effect at the openings. When the hair is wound up, the winding mandrel continues to rotate. The hair which does not continue to rotate with it slides on the rotating winding mandrel. Normally the friction force between the rotating winding mandrel and the hair which does not turn with it is so low that the traction exerted upon the hair by the friction force is not felt unpleasantly. In individual cases it may be however that the torque is too great so that "pulling" on the hair is unpleasantly felt. For this purpose the cited published document discloses that the winding mandrel is to be driven via a friction or sliding coupling so that if the hair catches on the winding mandrel for any reason, a mechanical torque limitation occurs.
This known torque limitation does not always function satisfactorily. This is because it is based, as the very terms sliding coupling or friction coupling express, upon the fact that two elements rub against each other when a certain torque is exceeded. However these conditions depend very much on outside factors such as for example the chemical composition of the ambient atmosphere. It may also occur that the hair catches in the suction openings of the winding mandrel. The traction force can also increase when the hair is very wet. Furthermore, special conditions may exist when long or especially thin hair is involved, or when a person is especially sensitive.
It is therefore the object of the instant invention to provide a device of the type mentioned initially so that the torque exerted by the winding mandrel upon the wound-up hair may be limited, with an especially high degree of safety in a reliable and simple manner, to a definite adjustable value.